Many things contribute to cancer, and much about the disease remains unknown. But this much is clear: environmental factors play an important role. When humans are exposed to certain substances in the workplace or at home, or in the food and water they consume, their risk of getting cancer can increase. And, of course, cigarette smoking plays a huge role as well. According to most recent data, overall cancer rates in the Bay Area are decreasing, particularly in men, likely due to a decrease in tobacco use. But breast cancer rates in the Bay Area remain among the world's highest.

Findings
NRDC researchers, relying on data gathered by the Cancer Registry of Northern California, examined rates of cancer in the Bay Area -- specifically, the incidence of new cancer cases per 100,000 people in the Bay Area between 1991 and 1997. (Numbers were adjusted to account for the age of the underlying population, because cancer risk increases with age.) NRDC researchers focused on types of cancer thought to have environmental components, including cancers of the brain and nervous system, breast, lung, and prostate, as well as leukemia and non-Hodgkin's lymphoma. Data were also examined by gender and race.

Overall, cancer rates in the Bay Area are decreasing, likely because of a decrease in tobacco use among Californians. Tobacco has been identified as the most important environmental cause of cancer, so as Bay Area residents reduce their use of it, lung cancer rates drop. Breast cancer rates in the Bay Area, on the other hand, are among the highest in the world.